DOI: 10.1148/rg.275075045
Physics of Cardiac Imaging with Multiple-Row Detector CT1
Mahadevappa Mahesh, MS, PhD and
Dianna D. Cody, PhD
1 From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, 601 N Caroline St, Baltimore, MD 21287-0856 (M.M.); and the Department of Imaging Physics, University of Texas M. D. Anderson Cancer Center, Houston, Tex (D.D.C.). From the AAPM/RSNA Physics Tutorial at the 2005 RSNA Annual Meeting. Received March 12, 2007; revision requested April 4 and received May 21; accepted June 8. M.M. receives research support from Siemens; D.D.C. is a speaker for the Medical Technology Management Institute, Milwaukee, Wis.
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Figure 1. Diagram shows the range of diastolic regions for varying heart rates. The desired temporal resolution for cardiac CT is approximately 250 msec for average heart rates of less than 70 beats per minute; for higher heart rates, the desired temporal resolution is approximately 100 msec.
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Figure 2. During the prospective ECG-triggered scan mode, the patient’s ECG is continuously monitored but the x-rays are turned on at predetermined R-R intervals to acquire sufficient scan data for image reconstruction. The table is then moved to the next location for further data acquisition. These types of scans are always sequential and not helical and result in a lower patient dose because the x-rays are on for a limited period. Calcium scoring scans are typically performed in this scan mode.
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Figure 3. During the retrospective ECG-gated scan mode, the patient’s ECG is continuously monitored and the patient table moves through the gantry. The x-rays are on continuously, and the scan data are collected throughout the heart cycle. Retrospectively, projection data from select points within the R-R interval are selected for image reconstruction. Radiation dose is higher in this type of scan mode compared with that in the prospective triggering mode. Pos = position.
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Figure 4. Differences between partial scan reconstruction versus multiple-segment reconstruction. Top: During partial scan reconstruction, sufficient data from a prescribed time range within the R-R interval of one cardiac cycle are selected for reconstruction. Bottom: In multiple-segment reconstruction, sufficient data segments of the same phase from multiple cardiac cycles are selected for image reconstruction. Higher temporal resolution (TR) can be achieved with this type of reconstruction.
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Figure 5a. Effect of temporal resolution on reconstructed images from the same patient. (a) Partial scan reconstruction with temporal resolution of approximately 250 msec. (b) Multiple-segment reconstruction (two segments) yields a temporal resolution of approximately 105 msec. The stair-step artifacts are less visible and the structures in the sagittal plane have a smooth edge compared with the appearance of partial scan reconstruction.
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Figure 5b. Effect of temporal resolution on reconstructed images from the same patient. (a) Partial scan reconstruction with temporal resolution of approximately 250 msec. (b) Multiple-segment reconstruction (two segments) yields a temporal resolution of approximately 105 msec. The stair-step artifacts are less visible and the structures in the sagittal plane have a smooth edge compared with the appearance of partial scan reconstruction.
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Figure 7a. Images from cardiac CT angiography (a) and fluoroscopically guided coronary angiography (b) show a right coronary artery (long arrow) with calcification (short arrows). The spatial resolution and delineation of details of CT angiography are comparable with those of coronary angiography. (Reprinted, with permission, from reference 8).
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Figure 7b. Images from cardiac CT angiography (a) and fluoroscopically guided coronary angiography (b) show a right coronary artery (long arrow) with calcification (short arrows). The spatial resolution and delineation of details of CT angiography are comparable with those of coronary angiography. (Reprinted, with permission, from reference 8).
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Figure 8a. Effect of reconstruction interval on image quality. All three sets of images are from the same data set reconstructed with 0.5-mm section thickness. However, the reconstruction intervals are different, which affects the number of reconstructed images and 3D image quality. (a) A reconstruction interval of 0.3 mm yields 301 images and implies a 60% overlap. (b) A reconstruction interval of 5 mm yields only 19 images and results in a staggered appearance of 3D images. (c) A reconstruction interval of 0.5 mm yields 184 images and results in image quality similar to that of a. Normally, a 50% overlap is sufficient for optimum image quality for MPR and 3D images.
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Figure 8b. Effect of reconstruction interval on image quality. All three sets of images are from the same data set reconstructed with 0.5-mm section thickness. However, the reconstruction intervals are different, which affects the number of reconstructed images and 3D image quality. (a) A reconstruction interval of 0.3 mm yields 301 images and implies a 60% overlap. (b) A reconstruction interval of 5 mm yields only 19 images and results in a staggered appearance of 3D images. (c) A reconstruction interval of 0.5 mm yields 184 images and results in image quality similar to that of a. Normally, a 50% overlap is sufficient for optimum image quality for MPR and 3D images.
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Figure 8c. Effect of reconstruction interval on image quality. All three sets of images are from the same data set reconstructed with 0.5-mm section thickness. However, the reconstruction intervals are different, which affects the number of reconstructed images and 3D image quality. (a) A reconstruction interval of 0.3 mm yields 301 images and implies a 60% overlap. (b) A reconstruction interval of 5 mm yields only 19 images and results in a staggered appearance of 3D images. (c) A reconstruction interval of 0.5 mm yields 184 images and results in image quality similar to that of a. Normally, a 50% overlap is sufficient for optimum image quality for MPR and 3D images.
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Figure 9. Pitch is defined as the ratio of table feed per gantry rotation to the total x-ray beam width. This definition is applicable to both single-row detector CT and multiple-row detector CT (21). I = table travel (millimeters) per rotation, N = number of active data acquisition channels, T = single data acquisition channel width (millimeters), W = beam width (millimeters).
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Figure 10. Graphs demonstrate the necessity for scanning at low pitch values during helical cardiac CT data acquisition. If the table feed becomes greater than the beam width, it results in a data gap, which is detrimental for image reconstruction.
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Figure 12a. Banding artifacts due to an increased heart rate from 51 to 69 beats per minute. Coronal (a) and sagittal (b) reformatted images of the heart obtained from CT data show banding artifacts (arrowheads). (Reprinted, with permission, from reference 29).
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Figure 12b. Banding artifacts due to an increased heart rate from 51 to 69 beats per minute. Coronal (a) and sagittal (b) reformatted images of the heart obtained from CT data show banding artifacts (arrowheads). (Reprinted, with permission, from reference 29).
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Figure 13a. Artifacts due to incomplete breath holding. (a) Axial images show no motion artifacts. (b, c) Coronal (b) and sagittal (c) reformatted images show banding artifacts. (Reprinted, with permission, from reference 29).
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Figure 13b. Artifacts due to incomplete breath holding. (a) Axial images show no motion artifacts. (b, c) Coronal (b) and sagittal (c) reformatted images show banding artifacts. (Reprinted, with permission, from reference 29).
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Figure 13c. Artifacts due to incomplete breath holding. (a) Axial images show no motion artifacts. (b, c) Coronal (b) and sagittal (c) reformatted images show banding artifacts. (Reprinted, with permission, from reference 29).
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Figure 14a. Streak artifacts visible in the presence of a stent. Thin-slab maximum intensity projection image (a), MPR image (b), and thin-slab maximum intensity projection image obtained with a wide window (c) show streak artifacts (arrows in a). (Reprinted, with permission, from reference 29).
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Figure 14b. Streak artifacts visible in the presence of a stent. Thin-slab maximum intensity projection image (a), MPR image (b), and thin-slab maximum intensity projection image obtained with a wide window (c) show streak artifacts (arrows in a). (Reprinted, with permission, from reference 29).
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Figure 14c. Streak artifacts visible in the presence of a stent. Thin-slab maximum intensity projection image (a), MPR image (b), and thin-slab maximum intensity projection image obtained with a wide window (c) show streak artifacts (arrows in a). (Reprinted, with permission, from reference 29).
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Copyright © 2007 by the Radiological Society of North America.
